Due to the abnormality of a refractive index of the lens or deterioration in adjustment performance thereof, the abnormality of a form of the eyeball, or the like, ametropia of an eye such as presbyopia, myopia, or hyperopia occurs. Among them, the presbyopia refers to a state in which adjustment performance of the lens is weakened by aging and thus the lens cannot focus on a near object. In order to correct the presbyopia, presbyopia spectacles formed of convex lenses are mainly used. If the presbyopia spectacles are used, a near object can be seen clearly, but there is a problem in that a far object cannot be seen clearly. In addition, in order to solve this problem, the presbyopia spectacles are worn when a near object is seen, and the presbyopia spectacles are taken off when a far object is seen, but there is a problem in that this is troublesome.
In relation to this problem, as spectacles which correct the presbyopia and also enable a far object to be seen clearly, there are so-called bifocal spectacles in which lenses with different degrees for far sight and near sight are combined with each other. For example, PTL 1 discloses bifocal spectacles in which a degree for far sight is used in the entire lens, and a degree for near sight is used at a part of a lower side of the lens. If these spectacles are used, a near object and a far object can be seen clearly with a pair of spectacles. However, since the degrees for far sight and near sight are discontinued at a boundary thereof, there is a problem in that an object is seen doubly around the boundary.
In contrast, PTL 2 discloses progressive multi-focal spectacles in which a degree gradually changes when coming toward a lower side of a lens. In these spectacles, degrees for far sight and near sight continuously change at a boundary thereof, and thus the discontinuity does not occur at the boundary.
In addition, PTLs 3 and 4 disclose varifocal spectacles which include lenses of which degrees (refractive indexes) can be changed and a control unit for changing the degrees. If these spectacles are used, a near object and a far object can be seen clearly with a pair of spectacles.